New York (CNN) -- A Bosnian-American who has been charged in an FBI terror inquiry "provided very detailed information" about his "terrorist-related activities" after waiving his right to a lawyer, federal prosecutors said.

Adis Medunjanin, 25, has pleaded not guilty to charges of conspiracy to commit murder in a foreign country and receiving military-type training from al Qaeda. Officials say he is an associate of Najibullah Zazi, who is accused of conspiring to use weapons of mass destruction on U.S. soil.

In a letter to Judge Raymond J. Dearie, filed Friday, federal prosecutors said Medunjanin spoke to authorities three times about the "terrorist-related activities of himself and others in the United States and Pakistan" after he waived his right to a lawyer.

"Prior to questioning ... the agents read the defendant his Miranda rights, which he waived orally and in writing," the letter said. It described the first session with Medunjanin, which occurred in a hospital after he crashed his car on New York's Whitestone Expressway.

"In addition, the agents specifically advised the defendant that they were aware that he was represented by an attorney, and asked the defendant if he wished to speak with them despite being represented. The defendant informed the agents that he was willing to answer their questions without an attorney, and added that he no longer wished to be represented by Robert Gottlieb," the letter said.

All of the sessions occurred before Medunjanin's January 8 indictment, according to the letter.

Gottlieb had argued in a letter to the judge filed Monday that his client was "intentionally and improperly hidden from his attorneys ... resulting in a coerced and invalid waiver of his right to our assistance as his longtime counsel."

Gottlieb said he has represented Medunjanin since September.

The attorney also asked the judge to sign subpoenas so that Gottlieb can file a motion to suppress alleged statements that Medunjanin made, according to the letter.

"It is our understanding that law enforcement obtained statements from Mr. Medunjanin ... [that] we expect the Government will seek to use in Mr. Medunjanin's prosecution, and which we intend to ask this Court to suppress in a pretrial motion."

He added, "It is our expectation that the records and materials we seek by these proposed subpoenas will establish both the efforts taken by law enforcement to move Mr. Medunjanin and secret him from his attorneys and to obtain an unlawful purported waiver of his right to the assistance of his attorney," the letter said.

In addition to speaking to agents from the Joint Terrorism Task Force in the hospital January 7, Medunjanin was interviewed later that day at the FBI offices in New York, the federal prosecutors said in their letter.

There, Medunjanin signed a waiver of his right to a speedy arraignment, the letter said. The waiver form included the charges against him and informed him of his Miranda rights, including his right to have an attorney present during questioning.

Medunjanin signed the waiver, the letter said.

The next day, Medunjanin again waived his Miranda rights orally and in writing, the letter said. "The defendant continued to provide the agents with information concerning his activities and the activities of others," the letter said.

After his indictment by a jury in the Eastern District of New York, federal prosecutors gave Medunjanin another speedy arraignment waiver, one that included an additional sentence, the letter said.

"Responding to a specific request from Mr. Gottlieb ... the government added the following language to the form ... 'I have been advised that attorney Robert Gottlieb has requested to speak with me,' " the letter said.

As agents were explaining the form to Medunjanin and telling him that he had been indicted, "the defendant expressed concerns about being charged with conspiracy to kill United States nationals abroad," the letter said.

"The defendant stated, in sum and substance, 'Maybe I should talk to Mr. Gottlieb,' and indicated this on the form," the letter said.

"At this point, agents ceased questioning," the letter said.

Medunjanin arrived in the United States in 1994 and became a citizen in 2002. Gottlieb has said his client and Zazi attended the same high school and frequented the same mosque.

Authorities say Zazi, who has pleaded not guilty to conspiracy charges, planned to use an explosive device in New York on September 11, 2009, the eighth anniversary of the U.S. terror attacks.

Another man said to be linked to Zazi, taxi driver Zarein Ahmedzay, has pleaded not guilty to lying to a federal agent, according to his attorney, Michael Marinaccio.

Ahmedzay and Medunjanin, residents of the New York borough of Queens, had been under surveillance.